Method for forming integrated circuit

ABSTRACT

A method for forming an integrated circuit includes following operations. A substrate having a first region, a second region and an isolation structure is received. A portion of the substrate is removed such that the second region is recessed. A portion of the isolation structure is removed to obtain a first top surface, a second top surface lower than the first top surface, and a boundary between the first top surface and the second top surface. A first device is formed in the first region, a second device is formed in the second region, and a dummy structure is formed over the first top surface, the second top surface and the boundary. A dielectric structure is formed over the substrate. A top surface of the first device, a top surface of the second device and a top surface of the dummy structure are aligned with each other.

PRIORITY DATA

This patent is a divisional application of U.S. patent application Ser. No. 16/732,230 filed Dec. 31, 2019, entitled of “BOUNDARY SCHEME FOR SEMICONDUCTOR INTEGRATED CIRCUIT AND METHOD FOR FORMING AN INTEGRATED CIRCUIT,” which is incorporated herein by reference in its entirety.

BACKGROUND

In the semiconductor art, it is desirable to improve transistor performance as devices become smaller due to ongoing reductions in device scale. Further, it is desirable to manufacture integrated circuit (“IC”) semiconductor devices that incorporate transistors for low, high and sometimes medium voltage range applications in a single integrated circuit. For example, transistors for logic functions, which operate at relatively low voltages, and transistors for high power applications, which operate at relatively high voltages, may be designed and fabricated on the same IC.

The transistors operating in two different voltage ranges are located on different regions of the IC, and use of shallow trench isolation (STI) is a typical approach that allows the regions for various types of transistors to be integrated onto the IC by creating electrically isolated regions within a single substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the following detailed description when read with the accompanying figures. It is noted that, in accordance with the standard practice in the industry, various features are not drawn to scale. In fact, the dimensions of the various features may be arbitrarily increased or reduced for clarity of discussion.

FIG. 1 is a flowchart representing a method for forming an integrated circuit according to aspects of the present disclosure.

FIGS. 2A to 2M are cross-sectional views illustrating stages of a method for forming an integrated circuit according to aspects of the present disclosure.

FIG. 3 is a top view illustrating an integrated circuit layout structure according to aspects of the present disclosure.

FIG. 4 is a top view illustrating an integrated circuit layout structure according to aspects of the present disclosure.

FIG. 5 is a cross-sectional view illustrating an integrated circuit according to aspects of the present disclosure.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, or examples, for implementing different features of the provided subject matter. Specific examples of components and arrangements are described below to simplify the present disclosure. These are, of course, merely examples and are not intended to be limiting. For example, the formation of a first feature over or on a second feature in the description that follows may include embodiments in which the first and second features are formed in direct contact, and may also include embodiments in which additional features may be formed between the first and second features, such that the first and second features may not be in direct contact. In addition, the present disclosure may repeat reference numerals and/or letters in the various examples. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and/or configurations discussed.

This description of illustrative embodiments is intended to be read in connection with the accompanying drawings, which are to be considered part of the entire written description. In the description of embodiments disclosed herein, any reference to direction or orientation is merely intended for convenience of description and is not intended in any way to limit the scope of the present disclosure. Relative terms such as “lower,” “upper,” “horizontal,” “vertical,” “above,” “below,” “up,” “down,” “top” and “bottom” as well as derivatives thereof (e.g., “horizontally,” “downwardly,” “upwardly,” etc.) should be construed to refer to the orientation as then described or as shown in the drawing under discussion. These relative terms are for convenience of description only and do not require that the apparatus be constructed or operated in a particular orientation. Terms such as “attached,” “affixed,” “connected” and “interconnected,” refer to a relationship wherein structures are secured or attached to one another either directly or indirectly through intervening structures, as well as both movable or rigid attachments or relationships, unless expressly described otherwise. Moreover, the features and benefits of the disclosure are illustrated by reference to the embodiments. Accordingly, the disclosure expressly should not be limited to such embodiments illustrating some possible non-limiting combination of features that may exist alone or in other combinations of features; the scope of the disclosure being defined by the claims appended hereto.

Notwithstanding that the numerical ranges and parameters setting forth the broad scope of the disclosure are approximations, the numerical values set forth in the specific examples are reported as precisely as possible. Any numerical value, however, inherently contains certain errors necessarily resulting from the standard deviation found in the respective testing measurements. Also, as used herein, the terms “substantially,” “approximately” or “about” generally mean within a value or range that can be contemplated by people having ordinary skill in the art. Alternatively, the terms “substantially,” “approximately” or “about” mean within an acceptable standard error of the mean when considered by one of ordinary skill in the art. People having ordinary skill in the art can understand that the acceptable standard error may vary according to different technologies. Other than in the operating/working examples, or unless otherwise expressly specified, all of the numerical ranges, amounts, values and percentages such as those for quantities of materials, durations of times, temperatures, operating conditions, ratios of amounts, and the likes thereof disclosed herein should be understood as modified in all instances by the terms “substantially,” “approximately” or “about.” Accordingly, unless indicated to the contrary, the, numerical parameters set forth in the present disclosure and attached claims are approximations that can vary as desired. At the very least, each numerical parameter should be construed in light of the number of reported significant digits and by applying ordinary rounding techniques. Ranges can be expressed herein as being from one endpoint to another endpoint or between two endpoints. All ranges disclosed herein are inclusive of the endpoints, unless specified otherwise.

Silicon-on-insulator (SOI) substrate has been widely used in semiconductor manufacturing operations. Due to the advantages provided by SOI, such as low parasitic capacitance, lower noise, less short channel effect and better swing performance, high-voltage (HV) devices can be embedded with SOL technology for integration with HV devices and low-voltage (LV) devices.

Further, high-k metal gate (HKMG) technology is expected to play an important role in the next generation of CMOS devices. This technology incorporates a high-k dielectric, which reduces leakage and improves the dielectric constant. To help with fermi-level pinning and to allow the gate to be adjusted to low threshold voltages, a metal gate is used instead of a polysilicon gate. By combining the metal gate and high-k dielectric, HKMG technology reduces gate leakage, thereby increasing the transistor capacitance and allowing chips to function with reduced power needs. Thus, integrating HV and LV devices with HKMG is a technology that enables conventional scaling of the transistor as well as reduction in required stand-by power due to a reduction in gate leakage.

However, research has found that when integrating the HV device with the HKMG technology can cause, high-k dielectric residue at a boundary between the LV device and the HV device. The high-k dielectric residue may cause a contamination during the subsequent manufacturing operations.

The present disclosure therefore provides a boundary scheme for the integration of HV devices and LV devices with HKMG technology. In some embodiments, the present disclosure therefore provides a boundary scheme for the integration of HV devices and LV devices with high-k first and metal-gate last technology. In some embodiments, a dummy structure such as a dummy polysilicon structure can be disposed on the boundary between a region accommodating the HV devices and a region accommodating the LV devices. The dummy structure is provided to entirely seal the high-k dielectric residue that is generated during manufacturing operations, and thus the high-k residue contamination can be mitigated.

In some embodiments, the high voltage (HV) devices used herein are referred to as devices, such as integrated circuit die input/output (I/O) devices, that generally have operating voltages greater than those of logic devices. For example, HV devices can have operating voltages greater than approximately 2.5 volts, while the logic devices can have operating voltages less than approximately 1.2 volts. In some embodiments, logic devices that have relatively low operating voltages are referred to as LV devices. However, operating voltages can vary for different applications, thus they are not limited herein.

FIG. 1 is a flowchart representing a method for forming an integrated circuit 10 according to aspects of the present disclosure. The method 10 includes a number of operations (101, 102, 103, 104, 105, 106, 107, 108, 109 and 110). The method 10 will be further described according to one or more embodiments. It should be noted that the operations of the method 10 may be rearranged or otherwise modified within the scope of the various aspects. It should be further noted that additional processes may be provided before, during, and after the method 10, and that some other processes may be only briefly described herein. Thus, other implementations are possible within the scope of the various aspects described herein.

FIGS. 2A to 2M are cross-sectional views illustrating stages of a method for forming an integrated circuit according to aspects of the present disclosure. At operation 101, a substrate 200 having a first region 202 a, a second region 202 b and an isolation structure 210 separating the first region 202 a from the second region 202 b is received or provided. In some embodiments, the first region 202 a can be used to accommodate LV devices such as logic devices, while the second region 202 b can be used to accommodate HV devices such as I/O devices, but the disclosure is not limited thereto. In some embodiments, the isolation structure 210 is formed to surround the first region 202 a and the second region 202 b such that at least a portion of the isolation structure 210 is disposed between the first region 202 a and the second region 202 b, as shown in FIG. 2A. Accordingly, the first region 202 a and the second region 202 b are electrically separated from each other by the isolation structure 210. In some embodiments, the isolation structure 210 can be a shallow trench isolation (STI), but the disclosure is not limited thereto.

In some embodiments, the substrate 200 can be a silicon-on-insulator (SOI) substrate. As shown in FIG. 2A, the substrate 200 can include a semiconductor bulk 204, a semiconductor layer 208 and a dielectric layer 206 disposed between the semiconductor bulk 204 and the semiconductor layer 208. In some embodiments, the semiconductor layer 208 can include a semiconductor material such as silicon, germanium, silicon germanium, or combinations thereof, but the disclosure is not limited thereto. In some embodiments, the dielectric layer 206 may be, for example, a buried oxide (BOX) layer or a silicon oxide layer, but the disclosure is not limited thereto. In some embodiments, the semiconductor bulk 204 can include silicon, but the disclosure is not limited thereto. In other embodiments, substrates that may be used include multi-layered substrates, gradient substrates, or hybrid orientation substrates. In some embodiments, a sum of a thickness of the semiconductor layer 208 and a thickness of the dielectric layer 206 can be between approximately 200 angstroms and approximately 50 angstroms, but the disclosure is not limited thereto. In some embodiments, devices formed over the SOI substrate can be referred to as SOI devices. In addition to the ability to retain low intra-well and inter-well leakage currents, the dielectric layer 206 also permits smaller distance for isolation spacing, thus permitting increased packing density. Additional advantages of SOL devices with respect to bulk devices include: reduced soft error sensitivity, improved turn-on characteristic, reduced leakage current, and improved reliability by eliminating junction spiking.

At operation 102, a portion of the substrate 200 is removed such that the second region 202 b is recessed, and a portion of the isolation structure 210 is removed such that the isolation structure 210 obtains a first top surface 212 a, a second top surface 212 b lower than the first top surface 212 a, and a boundary between the first top surface 212 a and the second top surface 212 b. As shown in FIG. 2B, in some embodiments, a patterned mask 211 such as a patterned photoresist can be formed over the substrate 200. A suitable etching operation can be performed to remove a portion of the substrate 200 in the second region 202 b and a portion of the isolation structure 210 exposed through the patterned mask 211. In some embodiments, a portion of the semiconductor layer 208 and a portion of the dielectric layer 206 in the second region 202 b are removed, such that the semiconductor bulk 204 is exposed. In other embodiments, a portion of the semiconductor layer 208, a portion of the dielectric layer 206 and a portion of the semiconductor bulk 204 in the second region 202 b are removed. Consequently, a recessed second region 202 b′ is obtained as shown in FIG. 2B.

Further, the portion of the isolation structure 210 exposed through the patterned mask 211 is removed, wherein a thickness of the removed portion of the isolation structure 210 is similar to a thickness of the removed portion of the substrate 200. Consequently, the isolation structure 210 obtains a first top surface 212 a, a second top surface 212 b and a boundary between the first top surface 212 a and the second top surface 212 b. The second top surface 212 b is lower than the first top surface 212 a. Further, the first top surface 212 a of the isolation structure 210 and a top surface of the substrate 200 in the first region 202 a are aligned with each other, or are at the same level, while the second top surface 212 b of the isolation structure 210 and a top surface of the substrate 200 in the second region 202 b′ are aligned with each other, or are at the same level. As shown in FIG. 2B, a step height H is formed at the boundary between the first top surface 212 a and the second top surface 212 b of the isolation structure 210. In some embodiments, the step height H can be equal to or greater than the thickness of the removed portion of the substrate 200. For example, when the etching operation is performed to remove the portion of the semiconductor layer 208 and the portion of the dielectric layer 206 in the second region 202 b′, the step height H is equal to or greater than the sum of the thickness of the semiconductor layer 208 and the thickness of the dielectric layer 206, such as between approximately 200 angstroms and approximately 500 angstroms, but the disclosure is not limited thereto. The patterned mask 211 can then be removed.

As shown in FIG. 2C, in some embodiments, a sacrificial insulating layer 213 is formed to completely cover the substrate 200. After the forming of the sacrificial insulating layer 213, a well region 220 can be formed in the substrate 200 in the second region 202 b′. In some embodiments, an implantation and an anneal can be performed on the semiconductor bulk 204 in the second region 202 b′. Consequently, the well region 220 is obtained. In some embodiments, the sacrificial insulating layer 213 helps to protect the substrate 200 in the first region 202 a and the isolation structure 210 and to mitigate an outgassing issue during the forming of the well region 220. In some embodiments using an n-type HV device, the well region 220 can have n-type dopants. In some embodiments, the well region 220 can be referred to as a drift region. In some embodiments, the drift region is between a device channel (e.g., under a gate structure to be formed) and a drain region to be formed. The drift region is configured to provide a high device breakdown voltage and protection from hot-carrier injection (HCI).

Referring to FIG. 2D, after the forming of the well region 220, a body region 222 is formed. The body region 222 can be disposed in the well region 220. In embodiments using an n-type HV device, the body region 222 can have p-type dopants that are opposite to that of the well region 220. In some embodiments, a body contact region (not shown) can be formed in the body region 222. The body contact region can have the same type of dopants as the body region 222. The body contact region can provide an electrical connection for the body region 222. It should be understood that the locations of the well region 220 and the body region 222 (and the body contact region) shown in FIG. 2D are merely exemplary, and one having skill in the art can modify them to achieve a desired HV device.

Still referring to FIG. 2D, after the forming of the body region 222, a well region 224 is formed in the substrate 200 in the first region 202 a. In some embodiments, the well region 224 is formed in the semiconductor layer 208 in the first region 202 a. In other embodiments, the well region 224 is formed in both of the semiconductor layer 208 and the semiconductor bulk 204. Additionally, depending on the type of the LV device to be formed, the well region 224 can include n-type or p-type dopants. In some embodiments, a well implantation is performed, and the sacrificial insulating layer 213 is subsequently removed. Before the removing of the sacrificial insulating layer 213, an anneal is performed. Consequently, the well region 224 for the LV device is obtained.

At operation 103, a high-k gate dielectric layer 228 is formed over the substrate 200. In some embodiments, prior to the forming of the high-k gate dielectric layer 228, an interfacial layer (IL) 226 can be formed on the substrate 200. One example of the IL 226 is a thin silicon oxide layer. In some embodiments, the thin silicon oxide layer can be formed by thermal oxidation. In other embodiments, the thin silicon oxide layer can be formed by atomic layer deposition (ALD). When the thermal oxidation is utilized to form the IL 226, the IL 226 is formed only on a top surface of the semiconductor material. Therefore, the IL 226 is formed on the semiconductor layer 208 in the first region 202 a and on the semiconductor bulk 204 in the second region 202 b′, while the isolation structure 210 is free of the IL 226, as shown in FIG. 2E. In other words, the IL 226 is formed on the well region 224 in the first region 202 a and on the drift region 220 and the body region 222 in the second region 202 b′. It has been observed that the IL 226 may provide a remedy for some high-k dielectric gate stack integration issues, such as carrier trapping by HK and carrier mobility reduction. The IL 226 may also be important as a diffusion barrier to prevent undesirable interface reactions between the HK dielectric material and the substrate 200.

Still referring to FIG. 2E, the high-k gate dielectric layer 228 can be formed on the IL 226 by ALD, chemical vapor deposition (CVD), metal organic CVD (MOCVD), physical vapor deposition (PVD), thermal oxidation, combinations thereof, or other suitable techniques. In some embodiments, the high-k gate dielectric layer 228 may include a binary or ternary high-k film such as HfO_(X). In some embodiments, the high-k gate dielectric layer 228 may include high-k material such as LaO, AlO, ZrO, TiO, Ta₂O₅, U₂O₃, SiTiO₃ (STO), BaTiO₃ (BTO), BaZrO, HfZrO, HfLaO, HfSiO, LaSiO, AlSiO, HfTaO, HMO, (Ba,Sr)TiO₃ (BST), Al₂O₃, Si₃N₄, oxynitrides, or other suitable materials.

At operation 104, a semiconductor layer 230 is formed on the high-k gate dielectric layer 228. In some embodiments, the semiconductor layer 230 can be a polysilicon layer disposed over the high-k gate dielectric layer 228 by deposition techniques. In other embodiments, the semiconductor layer 230 can be an amorphous silicon layer.

At operation 105, the semiconductor layer 230 and the high-k gate dielectric layer 228 are patterned to form a first sacrificial gate 232 a in the first region 202 a, a second sacrificial gate 232 b in the second region 202 b′ and a dummy structure 232 c on the isolation structure 210. As shown in FIG. 2F, a patterned hard mask 231 is formed over the semiconductor layer 230 to define locations and dimensions of the sacrificial gates, and an etching operation is performed to remove portions of the semiconductor layer 230 and the high-k gate dielectric layer 228. Consequently, the first sacrificial gate 232 a is firmed in the first region 202 a, the second sacrificial gate 232 b is formed in the second region 202 b′, and the dummy structure 232 c is obtained. Further, the dummy structure 232 c covers a portion of the first top surface 212 a of the isolation structure 210, a portion of the second top surface 212 b of the isolation structure 210, and a boundary between the first top surface 212 a and the second top surface 212 b, as shown in FIG. 2F. In some embodiments, thicknesses of the first sacrificial gate 232 a, the second sacrificial gate 232 b and the dummy structure 232 c are similar.

In some comparative embodiments, the semiconductor layer 230 and the high-k gate dielectric layer 228 over the isolation structure 210 are removed. However, it is found the high-k material at the boundary between the first top surface 212 a and the second top surface 212 b may not be removed completely due to the step height H. Further, the high-k residue may cause contamination issue in the subsequent manufacturing operations. In some comparative embodiments, the high-k gate dielectric layer may be over-etched in order to remove the high-k material from the boundary. However, it is found that the high-k gate dielectric layer under the sacrificial gate suffers from damage and a reliability issue is raised. In contrast to those comparative embodiments, the dummy structure 232 c is formed over the boundary of the first top surface 212 a and the second top surface 212 b, and therefore the high-k material (i.e., the high-k gate dielectric layer 228) is entirely covered by the semiconductor layer 230 of the dummy structure 232 c.

Further, a width of the dummy structure 232 c is greater than approximately 2 times a minimum critical dimension of the integrated circuit. It should be understood that the critical dimension (or the design rule limitation) defines the minimum width of a line or the minimum space between two lines permitted in the fabrication of a device. It should be noted that if the width of the dummy structure 230 c is less than 2 times the minimum critical dimension of the integrated circuit, the high-k material may be left over the boundary between the first top surface 212 a and the second top surface 212 b when the dummy structure 232 c is offset from the boundary due to process variation such as misalignment. Thus, the unwanted high-k residue issue occurs.

Referring to FIG. 2G, in some embodiments, a spacer 234 is formed over sidewalls of each of the first sacrificial gate 232 a, the second sacrificial gate 232 b and the dummy structure 232 c. As shown in FIG. 2F, the spacer 234 covers sidewalls of the patterned hard masks 231, the semiconductor layers 230, the high-k gate dielectric layers 228 and the ILs 226 of the first sacrificial gate 232 a and the second sacrificial gate 232 b. The spacer 234 also covers sidewalls of the patterned hard mask 231, the semiconductor layer 230 and the high-k gate dielectric layer 228 of the dummy structure 232 c. Therefore, the high-k gate dielectric layer 228 over the boundary between the first top surface 212 a and the second top surface 212 b can be entirely enclosed within the semiconductor layer 230 and the spacer 234 of the dummy structure 232 c, as shown in FIG. 2G. In some embodiments, the spacers 234 can be a multiple layered structure. For example, the spacers 234 can be an oxide-nitride (ON) structure including a silicon nitride sealing layer 234 a in contact with the ILs 226, the high-k gate dielectric layer 228, the semiconductor layers 230, and a silicon oxide layer 234 b covering the silicon nitride sealing layer 234 a, but the disclosure is not limited thereto.

Still referring to FIG. 2G, after the forming of the spacers 234, doped regions 236 a and 236 b are formed in the substrate 200. The doped regions 236 a and 236 b serve as a source region and a drain region, respectively. In some embodiments, in the first region 202 a, the doped regions 236 a and 236 b are respectively formed in the substrate at two sides of the first sacrificial gate 232 a. In some embodiments, in the second region 202 b, the doped regions 236 a and 236 b are formed in the body region 222 and the drift region 220, respectively. For example, as shown in FIG. 2G, the doped region 236 a is formed in the body region 222 while the doped region 236 b is formed in the drift region 220 and separated from the dummy structure 232 b by the drift region 220. Accordingly, at operation 106, a first device 240 a is formed in the first region 202 a, a second device 240 b is formed in the second region 202 b′, and a dummy structure 240 c is formed on the isolation structure 210. As shown in FIG. 2G, the dummy structure 240 c covers a portion of the first top surface 212 a, a portion of the second top surface 212 b and the boundary between the first top surface 212 a and the second top surface 212 b. Thereafter, a protecting layer 237 such as a resist protective oxide (RPO) layer can be formed to cover a portion of the second device 240 b, a portion of the doped region 236 b and a portion of the drift region 220. Subsequently, a salicide layer 238 is formed over the exposed doped regions 236 a and 236 b, as shown in FIG. 2G. In some embodiments, after the forming of the salicide layer 238, the patterned hard masks 231 are removed.

At operation 107, a dielectric structure is formed over the substrate 200 to cover the first device 240 a, the second device 240 b and the dummy structure 240 c. In some embodiments, the dielectric structure can include a contact etch stop layer (CESL) 242 and an inter layer dielectric (ILD) 244, as shown in FIG. 2H. In some embodiments, the CESL 242 can include a material selected from silicon nitride, silicon carbide, or other dielectric materials. In some embodiments, the ILD 244 can be blanketly formed to a thickness sufficient to form a top surface higher than the top surfaces of first device 240 a, the second device 240 b and the dummy structure 240 c. The ILD 244 may be formed of an oxide using, for example, flowable chemical vapor deposition (FCVD). The ILD 244 may also be a spin-on glass formed using spin-on coating. In some embodiments, the ILD 244 may include phospho-silicate class (PSG), born-silicate glass (BSG), boron-doped phospho-silicate glass (BPSG), tetraethyl orthosilicate (TEOS) oxide, TiN, SiOC, or other low-k non-porous dielectric materials.

At operation 108, a portion of the dielectric structure, a portion of the first device 240 a, a portion of the second device 240 b and a portion of the dummy structure 240 c are removed. As shown in FIG. 2I, in some embodiments, a planarization, such as a chemical mechanical polishing (CMP) operation, is performed to remove the portion of the dielectric structure, i.e., a portion of the ILD 244 and a portion of the CESL 242. The CMP is also performed to remove a portion of the first sacrificial gate 232 a and a portion of the spacer 234 of the first device 240 a, a portion of the second sacrificial gate 232 b and a portion of the spacer 234 of the second device 240 b, and a portion of the semiconductor layer 230 and a portion of the spacer 234 of the dummy structure 240 c. Consequently, a top surface of the first device 240 a, a top surface of the second device 240 b and a top surface of the dummy structure 240 c are aligned with each other, or at a same level, as shown in FIG. 2I.

Referring to FIG. 2J, in some embodiments, a dielectric layer 245 is firmed over the dummy structure 240 c, but the first device 240 a in the first region 202 a and the second device 240 b in the second region 202 b′ are exposed through the dielectric layer 245. The dielectric layer 245 servers as a protective layer for providing protection during the subsequent operations. In some embodiments, the dielectric layer 245 can include materials similar to the ILD 244, but the disclosure is not limited thereto. A thickness of the dielectric layer 245 should be great enough to endure the subsequent operation.

At operation 109, the first sacrificial gate 232 a and the second sacrificial gate 232 b are removed. As shown in FIG. 2K, the first sacrificial gate 232 a (i.e., the semiconductor layer 230) is removed to form a first gate trench 246 a in the first region 202 a, and the high-k gate dielectric layer 228 is exposed through a bottom of the first gate trench 246 a. The second sacrificial gate 232 b (i.e., the semiconductor layer 230) is removed to form a second gate trench 246 b in the second region 202 b′, and the high-k gate dielectric layer 228 is exposed through a bottom of the second gate trench 246 b. In contrast to the portion of the semiconductor layer 230 in the first and second regions 202 a and 202 b′, which are removed, the semiconductor layer 230 over the isolation structure 210 (i.e., over the portion of the first top surface 212 a, the portion of the second top surface 212 b and the boundary between the first top surface 212 a and the second top surface 212 b) is protected by the dielectric layer 245.

At operation 110, a first metal gate 248 a is formed in the first gate trench 246 a and a second metal gate 248 b is formed in the second gate trench 246 b, as shown in FIG. 2L. In some embodiments, the first metal gate 248 a and/or the second metal gate 248 b can include at least a barrier metal layer, a work functional metal layer and a gap-filling metal layer. The barrier metal layer can include, for example but not limited to, TiN. The work function metal layer can include a single layer of TiN, TaN, TaAIC, TiC, TaC, Co, Al, TiAl, HfTi, TiSi, TaSi or TiAlC, or a multilayer of two or more of these materials, but is not limited thereto. For the n-channel FET, one or more of TaN, TaAlC, TiN, Tic, Co, TiAl, HfTi, TiSi and TaSi is used as the work function metal layer, and for the p-channel FET, one or more of TiAlC, Al, TiAl, TaN, TaAlC, TiN, TiC and Co is used as the work function metal layer. In some embodiments, the gap-filling metal layer can include conductive material such as Al, Cu, AlCu, or W, but is not limited to the above-mentioned materials. In some embodiments, another planarization such as CMP is performed to remove superfluous metal materials and the dielectric layer 245. Accordingly, a top surface of the first metal gate 248 a, a top surface of the metal gate 248 b, a top surface of the dummy structure 240 c and a top surface of the dielectric structure (including the CESL 242 and the ILD 244) are aligned with each other, or at the same level. However, a thickness of the second metal gate 248 b is greater than a thickness of the first metal gate 248 a. Further, the dummy structure 240 c may include a first portion 241-1 and a second portion 241-2 coupled to each other. A thickness of the first portion 241-1 is similar to the thickness of the first metal gate 248 a and a thickness of the second portion 241-2 is similar to the thickness of the second metal gate 248 b, as shown in FIG. 2L.

Referring to FIG. 2M, in some embodiments, another ILD 250 may be formed over the substrate 200, and contact structures 252 may be formed in the ILD 250 and the ILD 244. Further, the contact structures 252 may penetrate the ILDs 250 and 244, such that the contact structures 252 are coupled to the doped regions 236 a and 236 b for providing electrical connection between the first and second devices 240 a and 240 b and other devices.

Accordingly, an integrated circuit 20 is provided. Please refer to FIGS. 3, 4 and 2M, wherein FIGS. 3 and 4 are top views illustrating an integrated circuit layout structure according to aspects of the present disclosure, and FIG. 2M is a cross-sectional view taken along lines A-A′, B-B′ and C-C′ of FIG. 3 and FIG. 4. The integrated circuit 20 includes a substrate 200, where the substrate 200 can be an SOI substrate including a semiconductor bulk 204, a semiconductor layer 208 and a dielectric layer 206 between the semiconductor bulk 204 and the semiconductor layer 208. A first region 202 a and a second region 202 b′ are defined in the substrate 200. In some embodiments, the second region 202 b′ is a recessed region such that a top surface of the substrate 200 in the second region 202 b′ is lower than a top surface of the substrate 200 in the first region 202 a. In some embodiments, the first region 202 a can be used to accommodate LV devices while the second region 202 b′ can be used to accommodate HV devices, and therefore the first region 202 a can be referred to as an LV region and the second region 202 b′ can be referred to as an HV region.

Further, the substrate 200 includes an isolation structure 210 disposed in the substrate 200 and separating the first region 202 a from the second region 202 b′. As shown in FIG. 2M, the isolation structure 210 has a first top surface 212 a and a second top surface 212 b lower than the first top surface 212 a. As mentioned above, the first top surface 212 a of the isolation structure 210 and the top surface of the substrate 200 in the first region 202 a are aligned with each other, or are at the same level, while the second top surface 212 b of the isolation structure 210 and the top surface of the substrate 200 in the second region 202 b′ are aligned with each other, or are at the same level. As shown in FIG. 2B, a step height H is formed at a boundary between the first top surface 212 a and the second top surface 212 b of the isolation structure 210, and the step height H is also formed between the first region 202 a and the second region 202 b′ of the substrate 200. In some embodiments, the step height H is equal to or greater than the sum of the thickness of the semiconductor layer 208 and the thickness of the dielectric layer 206, but the disclosure is not limited thereto.

The integrated circuit 20 includes a first device 240 a in the first region 202 a and a second device 240 b in the second region 202 b′. In some embodiments, the first device 240 a can be an LV device while the second device 240 b can be an HV device, but the disclosure is not limited thereto. Further, the integrated circuit 20 includes a semiconductor dummy structure 240 c disposed on the isolation structure 210. As shown in FIG. 2M, the semiconductor dummy structure 240 c covers a portion of the first top surface 212 a, a portion of the second top surface 212 b, and the boundary between the first top surface 212 a and the second top surface 212 b. In some embodiments, the semiconductor dummy structure 240 c is a frame-like structure. In some embodiments, the frame-like semiconductor dummy structure 240 c surrounds the first region 202 a, as shown in FIG. 3. In other embodiments, the frame-like semiconductor dummy structure 240 c surrounds the second region 202 b′, as shown in FIG. 4. A portion of the frame-like semiconductor dummy structure 240 c is disposed between the first region 202 a and the second region 202 b′, as shown in FIGS. 3, 4 and 2M. A width of the frame-like semiconductor dummy structure 240 c is less than a width of a portion of the isolation structure 210 between the first region 202 a and the second region 202 b′, as shown in FIGS. 3 and 4. Further, the width of the frame-like semiconductor dummy structure 240 c is greater than a width of the first device 240 a and a width of the second device 240 b, as shown in FIG. 2M.

Still referring to FIGS. 3 and 4, in some embodiments, the integrated circuit 20 further includes a frame-like doped region 214 disposed in the substrate 100. As shown in FIGS. 3 and 4, the frame-like doped region 214 may surround the second region 202 b′ and serve as a guard ring for the HV devices in the second region 202 b′. In some embodiments, the doped region 214 is separated from the second region 202 b′ by another isolation structure, though not shown. In some embodiments, the frame-like semiconductor dummy structure 240 c is disposed on the isolation structure 210 and surrounds the first region 202 a. Further, the frame-like semiconductor dummy structure 240 c is offset from the doped region 214, as shown in FIG. 3. In other embodiments, the frame-like semiconductor dummy structure 240 c is disposed on the isolation structure 210 but surrounds bath of the second region 202 b′ and the doped region 214. Further, the frame-like semiconductor dummy structure 240 c is offset from the doped region 214, as shown in FIG. 4.

Referring back to FIG. 2M, in some embodiments, the first device 240 a includes a first metal gate 248 a, a high-k gate dielectric layer 228 under the first metal gate 248 a, an IL 226 under the high-k gate dielectric layer 228, and doped regions 236 a and 236 b. The second device 240 b includes a second metal gate 248 b, a high-k gate dielectric layer 228 under the second metal gate 248 b, an IL 226 under the high-k gate dielectric layer 228, and doped regions 236 a and 236 b. in contrast to the first device 240 a and the second device 230 b, the semiconductor dummy structure 240 c includes a semiconductor layer 230 and a high-k gate dielectric layer 228 under the semiconductor layer 230. The first device 240 a further includes a spacer 234 disposed over sidewalls of the first metal gate 248 a, the high-k gate dielectric layer 228 and the IL 226. The second device 240 b further includes a spacer 234 disposed over sidewalls of the second metal gate 248 b, the high-k gate dielectric layer 228 and the IL 226. The semiconductor dummy structure 240 c further includes a spacer 234 disposed over sidewalls of the semiconductor layer 230 and the high-k gate dielectric layer 228. Accordingly, the high-k gate dielectric layer 228 of the semiconductor dummy structure 240 c is entirely enclosed within the semiconductor layer 230 and the spacer 234, as shown in FIG. 2M.

A thickness of the second device 240 b is greater than a thickness of the first device 240 a. The semiconductor dummy structure 240 c includes a first portion 241-1 and a second portion 241-2 coupled to each other, a thickness of the first portion 241-1 is similar to a thickness of the first device 240 a in the first region 202 a, and a thickness of the second portion 241-2 is similar to a thickness of the second device 240 b in the second region 202 b′. Because the thickness of the second device 240 b is greater than the thickness of the first device 240 a, the thickness of the second portion 241-2 of the semiconductor dummy structure 240 c is greater the thickness of the first portion 241-1 of the semiconductor dummy structure 240 c. Accordingly, top surfaces of the first device 240 a, the semiconductor dummy structure 240 c and the second device 240 b are aligned with each other, or at a same level.

In some embodiments, a width of the second device 240 b is greater than a width of the first device 240 a, and a width of the semiconductor dummy structure 240 c is greater than the widths of both the first device 240 a and the second device 240 b. In some embodiments, the width of the semiconductor dummy structure 240 c is greater than 2 times a minimum critical dimension (CD) of the integrated circuit. As mentioned above, the critical dimension (or the design rule limitation) defines the minimum width of a line or the minimum space between two lines permitted in the fabrication of devices. As mentioned above, if the width of the semiconductor dummy structure 240 c (i.e., the semiconductor layer 230) is less than 2 times the minimum critical dimension of the integrated circuit 20, the high-k material may be left over the boundary between the first top surface 212 a and the second top surface 212 b when the semiconductor dummy structure 240 c is formed offset from the boundary due to process variation such as misalignment. Thus, the unwanted high-k residue issue occurs.

Please refer to FIG. 5, which is a cross-sectional view illustrating an integrated circuit according to aspects of the present disclosure. It should be noted that same elements in FIGS. 2M and 5 are indicated by the same numerals, and details of the same elements shown in FIGS. 2M and 5 are omitted in the description of FIG. 5 for brevity. In some embodiments, the integrated circuit 20 includes another isolation structure 216 disposed in the second region 202 b′. The isolation structure 216 can be an STI or a field oxide (FOX). As shown in FIG. 5, a portion of the second metal gate 248 b and a portion of the high-k gate dielectric layer 228 cover a portion of the isolation structure 216.

The present disclosure therefore provides a boundary scheme for the integration of HV SOI devices and LV SOI devices with HKMG technology. In some embodiments, the present disclosure therefore provides a boundary scheme for the integration of HV SOI devices and LV SOI devices with high-k first and gate-last technology. In some embodiments, a dummy structure such as the semiconductor dummy structure is disposed on the boundary between the regions for accommodating the HV and LV devices. The semiconductor dummy structure is provided to entirely seal the high-k dielectric material that may be generated during the manufacturing operations, and thus the high-k residue contamination can be mitigated. Further, the method for forming the semiconductor dummy structure is compatible with and can be easily integrated in the manufacturing operations for SOI technology, HKMG technology and HV-LV integration.

According to one embodiment of the present disclosure, a method for forming an integrated circuit is provided. The method includes following operations. A substrate having a first region, a second region and an isolation structure separating the first region from the second region is received. A portion of the substrate is removed such that the second region is recessed, and a portion of the isolation structure is removed such that the isolation structure obtains a first top surface, a second top surface lower than the first top surface, and a boundary between the first top surface and the second top surface. A first device is formed in the first region, a second device is formed in the second region, and a dummy structure is formed over a portion of the first top surface, a portion of the second top surface, and the boundary between the first top surface and the second top surface. A dielectric structure is formed over the substrate to cover the first device, the second device and the dummy structure. A portion of the dielectric structure, a portion of the first device, a portion of the second device and a portion of the dummy structure are removed such that a top surface of the first device, a top surface of the second device and a top surface of the dummy structure are aligned with each other.

According to one embodiment of the present disclosure, a method for forming an integrated circuit is provided. The method includes following operations. A substrate is received. The substrate includes a first region, a second region and an isolation structure separating the first region and the second region. The isolation structure has a first top surface, a second top surface lower than the first top surface, and a boundary between the first top surface and the second top surface. A first device is formed in the first region, a second device is formed in the second region, and a dummy structure is formed on a portion of the first top surface, a portion of the second top surface and the boundary between the first top surface and the second top surface. A dielectric structure is formed over the substrate. A top surface of the dielectric structure, a top surface of the first device, a top surface of the second device, and a tops surface of the dummy structure are aligned with each other. A first metal gate is formed in the first region, and a second metal gate is formed in the second region.

According to one embodiment of the present disclosure, a method for forming an integrated circuit is provided. The method includes following operations. A substrate is received. The substrate includes a first region, a second region and an isolation structure separating the first region and the second region. The isolation structure has a first top surface, a second top surface lower than the first top surface, and a boundary between the first top surface and the second top surface. A first sacrificial gate is formed in the first region, a second sacrificial gate is formed in the second region, and a dummy structure is formed on a portion of the first top surface, a portion of the second top surface and the boundary between the first top surface and the second top surface. A first dielectric structure is formed over the substrate. A dielectric layer is formed over the dummy structure. The first sacrificial gate and the second sacrificial gate are exposed through the dielectric layer. The first sacrificial gate is replaced with a first metal gate, and the second sacrificial gate is replaced with a second metal gate. A second dielectric structure is formed over the first metal gate, the second metal gate, the dummy structure and the first dielectric structure.

The foregoing outlines features of several embodiments so that those skilled in the art may better understand the aspects of the present disclosure. Those skilled in the art should appreciate that they may readily use the present disclosure as a basis for designing or modifying other processes and structures for carrying out the same purposes and/or achieving the same advantages of the embodiments introduced herein. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the present disclosure, and that they may make various changes, substitutions, and alterations herein without departing from the spirit and scope of the present disclosure. 

What is claimed is:
 1. A method for forming an integrated circuit, comprising: receiving a substrate having a first region, a second region and an isolation structure separating the first region from the second region; removing a portion of the substrate and a portion of the isolation structure such that the second region is recessed and the isolation structure obtains a first top surface, a second top surface lower than the first top surface, and a boundary between the first top surface and the second top surface; forming a first device in the first region, a second device in the second region and a dummy structure on a portion of the first top surface, a portion of the second top surface, and the boundary between the first top surface and the second top surface; forming a dielectric structure over the substrate to cover the first device, the second device and the dummy structure; and removing a portion of the dielectric structure, a portion of the first device, a portion of the second device and a portion of the dummy structure such that a top surface of the first device, a top surface of the second device, and a top surface of the dummy structure are aligned with each other.
 2. The method of claim 1, wherein the substrate comprises a semiconductor bulk, a semiconductor layer and a dielectric layer disposed between the semiconductor bulk and the semiconductor layer, and the removing of the portion of the substrate removes a portion of the semiconductor layer and a portion of the dielectric layer in the second region such that the semiconductor bulk in the second region is exposed.
 3. The method of claim 1, wherein the forming of the first device, the second device and the dummy structure further comprises: forming a high-k gate dielectric layer over the substrate; forming a semiconductor layer on the high-k gate dielectric layer; and patterning the high-k gate dielectric layer and the semiconductor layer to form a first sacrificial gate in the first region, a second sacrificial gate in the second region, and the dummy structure on the isolation structure, wherein the dummy structure covers the portion of the first top surface, the portion of the second top surface, and the boundary between the first top surface and the second top surface, and thicknesses of the first sacrificial gate, the second sacrificial gate and the dummy structure are similar.
 4. The method of claim 3, further comprising: removing the first sacrificial gate and the second sacrificial gate to form a first gate trench and a second gate trench; and forming a first metal gate in the first gate trench and a second metal gate in the second gate trench, wherein a thickness of the second metal gate is greater than a thickness of the first metal gate.
 5. The method of claim 4, further comprising forming a dielectric layer over the dummy structure prior to the removing of the first sacrificial gate and the second sacrificial gate.
 6. The method of claim 4, wherein the dummy structure comprises a first portion and a second portion coupled to each other, a thickness of the first portion is similar to the thickness of the first metal gate, and a thickness of the second portion is similar to the thickness of the second metal gate.
 7. method for forming an integrated circuit, comprising: receiving a substrate having a first region, a second region and an isolation structure separating the first region from the second region, wherein the isolation structure has a first top surface, a second top surface lower than the first top surface, and a boundary between the first top surface and the second top surface; forming a first device in the first region, a second device in the second region and a dummy structure on a portion of the first top surface, a portion of the second top surface, and the boundary between the first top surface and the second top surface; forming a dielectric structure over the substrate, wherein a top surface of the dielectric structure, a top surface of the first device, a top surface of the second device, and a top surface of the dummy structure are aligned with each other; and forming a first metal gate in the first device and a second metal gate in the second device.
 8. The method of claim 7, wherein a top surface of the first region is aligned with the first top surface of the isolation structure, and a top surface of the second region is aligned with the second top surface of the isolation structure.
 9. The method of claim 7, wherein the forming of the first device, the second device and the dummy structure further comprises: forming a gate dielectric layer over the substrate; forming a semiconductor layer on the gate dielectric layer; and patterning the gate dielectric layer and the semiconductor layer to form a first sacrificial gate in the first region, a second sacrificial gate in the second region, and the dummy structure on the isolation structure, wherein the dummy structure covers the portion of the first top surface, the portion of the second top surface, and the boundary between the first top surface and the second top surface.
 10. The method of claim 9, wherein thicknesses of the first sacrificial gate, the second sacrificial gate and the dummy structure are similar.
 11. The method of claim 9, wherein the forming of the first metal gate in the first device and the second metal gate in the second device further comprises: removing the first sacrificial gate from the first device to form a first gate trench and the second sacrificial gate from the second device to form a second gate trench; and forming the first metal gate in the first gate trench and the second metal gate in the second gate trench, wherein a thickness of the second metal gate is greater than a thickness of the first metal gate.
 12. The method of claim 11, further comprising forming a dielectric layer over the dummy structure prior to the removing of the first sacrificial gate and the second sacrificial gate, wherein the first device and the second device are exposed through the dielectric layer.
 13. The method of claim 7, wherein the forming of the dielectric structure over the substrate further comprising: forming the dielectric structure to cover the first device, the second device and the dummy structure; and removing a portion of the dielectric structure, a portion of the first device, a portion of the second device and a portion of the dummy structure such that the top surface of the first device, the top surface of the second device, and the top surface of the dummy structure are aligned with each other.
 14. The method of claim 7, wherein the dummy structure comprises a first portion and a second portion coupled to each other, a thickness of the first portion is similar to the thickness of the first metal gate, and a thickness of the second portion is similar to the thickness of the second metal gate.
 15. A method for forming an integrated circuit, comprising: receiving a substrate having a first region, a second region and an isolation structure separating the first region from the second region, wherein the isolation structure has a first top surface, a second top surface lower than the first top surface, and a boundary between the first top surface and the second top surface; forming a first sacrificial gate in the first region, a second sacrificial gate in the second region and a dummy structure on a portion of the first top surface, a portion of the second top surface, and the boundary between the first top surface and the second top surface; forming a first dielectric structure over the substrate; forming a dielectric layer over the dummy structure, wherein the first sacrificial gate and the second sacrificial gate are exposed through the dielectric layer; replacing the first sacrificial gate with a first metal gate and the second sacrificial gate with a second metal gate; and forming a second dielectric structure over the first metal gate, the second metal gate, the dummy structure and the first dielectric structure.
 16. The method of claim 15, wherein the forming of the first sacrificial gate, the second sacrificial gate and the dummy structure further comprises: forming a dielectric layer over the substrate; forming a semiconductor layer on the dielectric layer; and patterning the dielectric layer and the semiconductor layer to form the first sacrificial gate in the first region, the second sacrificial gate in the second region, and the dummy structure on the isolation structure.
 17. The method of claim 15, wherein the forming of the first dielectric structure over the substrate further comprises: forming the first dielectric structure to cover the first sacrificial gate, the second sacrificial gate and the dummy structure; and removing a portion of the first dielectric structure to expose the first sacrificial gate and the second sacrificial gate such that a top surface of the first dielectric structure, a top surface of the first sacrificial gate, a top surface of the second sacrificial gate, and a top surface of the dummy structure are aligned with each other.
 18. The method of claim 15, wherein a top surface of the first metal gate, a top surface of the second metal gate, a top surface of the dummy structure, and a top surface of the first dielectric structure are aligned with each other.
 19. The method of claim 15, wherein the dummy structure comprises a first portion and a second portion coupled to each other, a thickness of the first portion is similar to the thickness of the first metal gate, and a thickness of the second portion is similar to the thickness of the second metal gate.
 20. The method of claim 15, further comprising forming contact structures in the second dielectric structure. 